NO. 36 NEW MAMMALS FROM PAN AM A— GOLDMAN 5 



terized by simpler dentition than Sciurus; the small cusps inter- 

 mediate in position between the larger tubercles on the outer side in 

 the large upper molariform teeth in Sciurus are absent in Micro- 

 sciunts. The skull of the type of venustuhis lacks the small anter- 

 ior premolar usually present in Micro sciurus. 



Specimens examined. — Total number, 3, from the following locali- 

 ties : 



Canal Zone: Gatun, 2. 



Panama: Porto Bello, i, 



ORYZOMYS IDONEUS, sp. nov. 



Type from Cerro Azul (altitude 2500 feet), near the headwaters 

 of the Chagres River, Panama. No, 171 106, female adult U. S. 

 National Museum (Biological Survey Collection), collected by E. A. 

 Goldman, March 26, 191 1. Original number 21010. 



General characters. — A large species of the subgenus Melanoniys, 

 allied to colnmbianus, but larger, with shorter tail ; color more rufes- 

 cent. Differing from phceopus and chrysomelas in larger size and 

 decidedly paler color. 



Color. — Upper parts cinnamon-rufous evenly mixed with black, 

 becoming somewhat paler along flanks ; outer sides of limbs dark 

 brownish cinnamon ; under parts dark tawny ochraceous, the under 

 color showing through ; feet and tail thinly haired, the hairs and 

 epidermis blackish. 



Skull. — Closely resembling that of columbianus, but decidedly 

 larger; sides of frontals more projecting as supraorbital shelves. 

 Differing from those of phceopus and chrysomelas mainly in decidedly 

 larger size. 



Measurements.— Type: Total length, 218 mm.; tail vertebree, 88; 

 hind foot, 30. Skull (type): Greatest length, 31.5; condylobasal 

 length, 29.5 ; zygomatic breadth, 17.5 ; nasals, L2.5 ; interorbital 

 breadth, 6.5 ; interparietal, 8.7 x 2.5 ; incisive foramina, 4.8 ; length 

 of palatal bridge, 6.5 ; maxillary toothrow, 4.8. 



Remarks. — A single specimen of -this rice rat was taken in the 

 humid forest on Cerro Azul. The group to which it belongs bears a 

 marked external resemblance to some species of Akodon, and this fact 

 probably led to the publication of Akodon columbianus Allen ( = 

 Oryzomys columbianus). 0. columbianus is closely allied to 0. 

 phceopus and 0. chrysomelas, and these forms, perhaps along with 

 the one described above, may prove to be intergrading geographic 

 races all assignable to a single widely ranging species. 



